Electrical protective device



Aug.` 3, 1943. K. H. BENTON ELECTRICAL PROTECTIVE DEVICE Filed Oct. l,1941 Inventor, Kenneth H. Benton, b y W His Attorney Patented Aug'. 3,1943 z,3zs,935

u 2,325,935 ELECTRICAL PROTECTIVE DEVICE Kenneth H. Benton, Pittsfield,Mass., assignor to General Electric Com New York pany, a corporation ofApplication October 1, 1941, Serial Nb. 413,163

9 Claims.

-ent 2,157,815, granted May 9, 1935 and assigned to the same assignee asthe present application.

Circuit-interrupting devices, such as circuit breakers, fuses, and thelike, quite often employ an arc-confining structure composed of orsurfaced with a gas-evolving insulating material, that is, a materialwhich, under the influence of the heat of the arc, emits gases or vaporsto aid,

at least in part, in extinguishing the arc. Numerous organic orinorganic gas-evolving insulatlng materials have been suggested for usewith electric circuit interrupters but most of these have certaindisadvantages, such as a tendency to become conducting because ofcarbonization when subjected to the heat of an arc. Vulcanized fiber haslong been accepted as a very efficient gas-evolvinginsulating materialfor use with circuit-interrupting devices since. it is not affected inthe disadvantageous manner indicated above by the heat of an arc as arethe other organic or inorganic materials referred to above. Suchvulcanized fiber or fibrous organic material has good mechanicalstrength together with the inherent ability to give olf large quantitiesof water vapor when exposed to the heat of an arc. However, when usedfor the casing-of expulsion tubes, fuses, or the like which are exposedto the weather, fiber absorbs water to such an extent that, unless atube or casing formed of such a material be protectively covered with amoisture resistant composition, the tube swells, warps, and

soon becomes useless. Also, the high degree of water absorption oforganic brous material tends to increase its rate of deterioration andthe progressive formation of aconducting and finally a carbonized path(tracking) across the outer surface of .the fuse tube. 'Ihis trackingoccurs, of course, only when voltage is maintained across the tubesurface, such as is the case after an expulsion fuse has blown.

To improve the weathering of fiber and also to lend mechanical supportagainst warping, it has been the general practice to cover a fiber fusetube, for example, with cloth or paper covered or filled with a resin,generally of the phenolic type. The use of fiber fuse tubes covered Witha phenolic covering, involving a cloth or paper base,

(Cl. 20o-127) necessitates an expensive process involving sev-k eralsteps, and the resulting covering of such heat-curable resins is oftenvery brittle and consequently has a low impact strength.

One object of my invention is to provide a new and improved electricprotective device.

y1t is another object of my invention to provide an arc-confiningstructure for electric circuit interrupters in which a fibrous organicmaterial is surfaces with a thermo-plastic cellulose derivative of theether or ester group.

Further objects and advantages of my invention will become apparent asthe following description proceeds and the features of novelty whichcharacterize my invention will be pointed out with particularity in theclaims annexed to and forming a part of this specification.

For a better understanding of my invention, reference may be had to theaccompanying drawing in which Fig. 1 is a sectional view of an electricprotective device embodying my invention, and Fig. 2 portrays one methodof constructing the fuse tube embodied in the protective deviceillustrated in Fig. 1.

Although my invention is applicable to circuit nterrupters in generalemploying gas-evolving insulating materials forzare-extinguishingpurposes, I have chosen to illustrate my invention specifically in Fig.l as applied to a fused protective device including an expulsion tubesurrounding a renewable fuse link. The fuse holder of the expulsion tubeof Fig. 1 is illustrated as comprising a tubular. casing, generallyindicated at I0 including an inner tube or liner I I constructed of agasevolving insulating material, preferably a fibrous organic materialsuch as vulcanized fiber or the like. Surrounding the inner tube orline` Il is a weatherproof surfacing material l2 which lends strength tothe inner tube I I. Such surfacing material which should be ofsubstantial thickness such that it may be machined without cuttingthrough said thickness is preferably composed of an extrudable ormoldable composition of a particular class of compounds which I havefound to be eminently suitable for this purpose. These compounds arewater-resistant or Water-insoluble cellulose derivatives selected fromthe class consisting of cellulose ethers and organic esters ofcellulose, as, for instance, ethyl cellulose, benzyl cellulose,cellulose acetate, cellulose propionate, cellulose butyrate, celluloseaceto-butyrate, etc. The tubular casing or holder I0 is provided withcontacts I3 and I4 which arey mounted on either end thereof forconnecting the fuse unit in the circuitA by mounting in a suitable fusesupport or otherwise. A cap i which closes one end of the casing lll isthreaded on to the contact i3, providing a clamped electrical contactwith the button head end it of the fuse link I'i. Other suitableclamping means it and l@ are provided for similarly clamping the lowerterminal 2t of the fuse link il to the contact lil.

By constructing the expulsion fuse tube or casing i@ inthe mannerindicated, the cellulose derivatives, which are thermoplastic, may beextruded on the fiber tube or molded thereon in a 'single operation ascontrasted with the much y more complicad and expensive process requiredaantast whether such structure is in the form of a tube or spaced apartplates or walls.

portion thereof surfaced with a coating of a celmaintaining theytheririoplastic material at the f proper temperature duringthe.extrusion process. The fiber tube l i is passed through the extrusionapparatus and the material 23 is forced around the tube ll. A suitablecentering guide 25, forming die 26, and forming dieholder 2l, mounted onthe extrusion apparatus, cause the material 23 to be extruded around bertube ll to produce the fuse tube l0 indicated in Fig. 1 by a singleoperation.

Although I have illustrated in Fig. 2 an extrusion apparatus for coatingthe' :ber tubes with .the `thermoplastic cellulose derivative, it shouldv be understood that this thermoplastic substance might also be moldedaround the ber tube.

It should be understood that suitable plasticizers may be used with theabove-mentioned coating materials in order to impart the desired degreeof'extrudability.

I have discoveredl that the thermoplastic surfacing material, referredto above, machines very satisfactorily so kthat threads may be cuttherein as indicated ln Fig. l, or any other suitable operation may beperformed thereon. Furthermore, such fiber tubes covered with one of theabove referred to cellulose derivativesvhave great impact strength tolwithstand the explosive action upon blowing of the fuse. Also, thismaterial provides a greater resistance to carbonization than materialused heretofore. I have also 'discovered that, by using thethermoplastic material set forth above in the manner indicated, a verysimple means for identifying fuse tubes for different purposes or ofdifferent ratings is obtained since various colored dies may be added tothe'thermoplastic 'cellulose derivative material.

It is to be understood that this invention is not limited to thespecific structures described andillustrated and the invention may beutilized with any type of circuit interruptor or fuse structure havingas an essential element an insulating member disposed adjacent to and inconlining relationship with an arc formed when the circuit is opened.The term arc-confining structure and similar terminology as used hereinand in the appended claims includes within its means any structuredisposed adjacent an arc lulose derivative selected from the classconsisting of water-resistant cellulose ethers and organic esters 'ofcellulose, said coating having 1a substantial thickness such that it maybe machined without cutting through said thickness.

2. An arc-confining structure comprising iibrous organic material havingthe outer portion thereof surfaced with a coating of'a cellulosederivative selected from the class consisting of Water-resistantcellulose ethers and organic esters of cellulose, said coating having asubstan tial thickness such that it may be machined without cuttingthrough said thickness. 3. An electric device having terminals betweenwhich an arc is formed and an insulating structure disposed adjacent toand in confining relationship with said arc, said insulating structurecomprising brous organic material having the outer portion thereofsurfaced with a coating of substantial thickness such that it may bemachined without cutting throughsaid thickness formed of a cellulosederivative selected from the class consisting of water-resistantycellulose ethers and organic esters of cellulose. 4. An electric circuitinterrupter comprising means for opening the circuit-so as to form anarc and an insulating structure disposed adjacent to and in confiningrelationship with said arc, said insulating structure having an outersurface comprising a coating of substantial thickness such that it maybe machined without cutting through said thickness formed of a cellulosederivative selected from the class consisting of water-insolublecellulose ethers and organic'esters of cellulose,

5. An expulsion fuse including an arc-conning structure formed of abrous organic material coated on the outside with a material comprisinga coating of substantial thickness such that it may be machined withoutcutting' through said thickness formed of a cellulose derivativeselected from the class consisting of water-insoluble cellulose ethersand organic esters of cellulose.

6. An electric device having terminals between which an arc is formedvand an insulating structure disposed adjacent to andin confiningrelationship with said arc, said insulating structure having the outersurface thereof covered with a coating of substantial thickness suchthat it may be machined without cutting through said thickness formed ofcellulose acetobutyrate.

7. An electric device having terminals between which an arc is formedand an insulating structure disposed adjacent to and in conningrelatlonship with said arc, said insulating structure having an outletsurface comprising a coating formed of cellulose acetate of substantialthickness such that it may be machined without cutting through saidthickness. Y

8. .An electric device having terminals between which an arc is formedand an insulating structure disposed adjacent to and in confining rela-Ationship with said arc, said insulating structure having an outletsurface of ethyl cellulose comprising a coating of substantial thicknesssuch that it may be machined without cutting through said thickness.

9. An edectric device having terminals between which an arc is formedand an insulating structure disposed adjacent to and in conningreiationshipwitn said arc, said insulating smicture comprising a fibrousorganic material covxered with an outer coating of substantial thicknesssuch that it may be machined without cutting through said thicknesscomprising an extruded cellulose derivative selected from the classconsisting of' water-insoluble cellulose ethers land organic esters ofcellulose.

KENNETH H. BENTON..

CERTIFICATE OF CORRECTION. Patent No. 2,525,955. August 5, 19145.

KENNETH s. ma'NfroN.

It is hereby certified that error appears in` the printed specificationof the above numbered patent requiring correction as follows: Page l,first column, line 6, for'arm" read -arc-; and second column, line l0,for surfaces read -surfaced; page 2, first column, line 75, for "means"read -meaning; and second column, line 70, and page 5, first column,line 5, for "outlet" read outer; line "I, for "edectric" read--electric; and that the said Letters Patent should be read with thiscorrection therein tha-t the same may conform to the record of the casein the Patent Office.

Signed and sealed this 12thA d ay of October, A. D. 19145.

Henry Van Arsdale, (Seal) Acting Commissioner of Patents.

CERTIFICATE OF CORRECTION.

patent No. 2,525,955. August 5, 19145.

KENNETH H. BENTON.A l

It is hereby certified that error appears in' the printed specificationof the above numbered patent requiring correction as follows: Page 1,first column, line 6, forarm" read --arc; and second column, line 10,for 'surfaces'l read .surfaced; page -2, first column, line "[5, for"means" read meaning; and second column, line 70, and page 5, firstcolumn, line 5, for "outlet'l read -outer; line 7, for "edectric" readelectric; and that the said Letters Patent should be read with thiscorrection therein tha-t the same may conform to the record of the casein the Patent Office.

Signed and sealed this l2th d ay of October, A. D. 1914.5.

Henry Van Arsdale, (Seal) Acting Commissioner of Patents.

